The present invention relates generally to lathe chuck jaws and more particularly to self-aligning lathe chuck jaws which better hold an imperfectly-shaped workpiece.
Lathe chucks hold a workpiece in a lathe using chuck jaws. Existing lathe chucks include a universal chuck and an independent chuck. The universal chuck usually has three jaws which are simultaneously and radially advanced to, or retracted from, the workpiece. The independent chuck usually has four jaws which are independently and radially moved to and from the workpiece. With both types of lathe chucks, each jaw is attached to a radially moving actuator, is rigid, is generally of a single-piece construction, and typically has a work-piece-gripping surface shaped to generally match the workpiece.
Existing jaws have difficulty in securely holding imperfectly-shaped workpieces. For example, where the workpiece is a cylindrical tube, the tube stock may be within specifications, but still be bent, bowed, out of round, with wall thickness variations, or with other deviations from true cylindrical form. This creates a situation in which the standard jaws allow the workpiece to slip during machining, or if tightened to prevent slippage can actually deform the tube. Presently, the machine operator must compensate for each imperfectly-shaped tube with shims, by time-consuming trial and error, and even then is not assured that the part will be acceptable when finished. The handling of shims can be a safety hazard. Also, it is difficult using standard jaws to hold an imperfectly-shaped workpiece close to the average lengthwise center line with the ends of the tube reasonably parallel. For work demanding close tolerances, the reject percentages can be high and costly.